Deflectors are used in various devices for deflecting a beam of charged particles in a desired direction or manner. An example of an apparatus employing deflectors is a scanning electron microscope in which an electron beam must be scanned at high speed and with high precision across the surface of a specimen.
Another example of an apparatus employing deflectors is an electron-beam transfer device used to reductively transfer a mask pattern defining, e.g., a semiconductor integrated circuit, onto the surface of a substrate, e.g., a semiconductor wafer. In such apparatus, a field-selection deflector is used to direct the electron beam onto a single mask subfield, among multiple subfields of a complete mask pattern to be transferred to the substrate. Deflectors are also used in such apparatus to direct the electron beam, after the beam has passed through the mask subfield, to the corresponding transfer subfield on the substrate surface.
Electromagnetic deflectors, used principally to deflect an electron beam using a magnetic field generated by a excitation coil, are primarily used in applications requiring the beam to be deflected with low aberration.
Prior-art excitation coils are formed by winding copper wire usually having a round or nearly square cross-section and having an insulative coating. Normally, deflectors operable to deflect a beam in one dimension include a pair of excitation coils opposing each other across an "optical axis." Such coils are usually disposed inside a cylindrical element made, e.g., from ferrite, thereby forming an electromagnetic deflector. Since it is normally necessary that the electron beam be independently deflectable in two orthogonal dimensions, many prior-art deflectors employ two pairs of coils, each pair being situated perpendicularly to the other pair.
In making prior-art electromagnetic deflectors as described above that include a pair of coils made by winding copper wire, it is difficult to position and attach the pair of coils to a cylindrical outer casing with a degree of accuracy demanded by modern applications. As a result, whenever the coils are energized with electric current, they frequently exhibit an unacceptable degree of deflection aberration (deflection distortion).
Prior-art electromagnetic deflectors intended for use in deflecting an electron beam in two perpendicular directions also frequently exhibit problems due to the difficulty in arranging the two pairs of coils precisely perpendicular to each other inside the outer casing. Representative problems with such deflectors include a tendency for the beam to not be deflected accurately in the desired direction(s).